[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: x99delaney1@xxxxxxxxxxx*Subject*: Re: PHREEQC*From*: "David L Parkhurst" <dlpark@xxxxxxxx>*Date*: Thu, 4 Sep 2003 10:03:22 -0600*Bcc*: "David L Parkhurst" <dlpark@xxxxxxxx>*In-reply-to*: <SEA2-F33KgFYAMgQSzP0003fd9b@hotmail.com>

Good, but you need to look at the output more carefully. SOLUTION 1 EQUILIBRIUM_PHASES 1 Calcite 0 10 CO2(g) -2.0 10 END SOLUTION 2 EQUILIBRIUM_PHASES 2 Calcite -1 10 CO2(g) -2.0 10 END > The differences between these two simulations are the changes in the saturation indices in the calcite at equilibrium. The concentrations stay the same. Concentrations are not the same. The above input file generates a printout of 4 solutions: (1) an initial solution calculation for solution 1, (2) a reaction calculation of solution 1 reacted with equilibrium_phases 1, (3) an initial solution calculation for solution 2, and (4) a reaction calculation of solution 2 reacted with equilibrium_phases 2. (1) and (3) are not very interesting, they show the distribution of species in pure water. (2) and (4) are the important sections of the output. Here is a section of output for (2). In this problem, equilibrium_phases contains 10 moles of Calcite and 10 moles of CO2 and we want to react enough in solution 1 to attain a saturation index of 0 for calcite and a partial pressure of -2 for CO2. (The log of the partial pressure is numerically equal to the value printed for saturation index.) 10 moles is sufficient to attain equilibrium with all but the most soluble phases, so we expect the output to have the saturation index and partial pressure that we specify, and indeed, the "Phase assemblage" output indicates SI=0 for calcite and -2 (= log partial pressure) for CO2 (SIs are also in the "Saturation Indices" section of the output). To reach this state, 1.646 mmol of calcite dissolved; the amount of calcite decreased from 10 moles to 9.998. 1.976 mmol of CO2 dissolved. The total C and Ca in solution 1 were 0 (pure water). The concentration of C is 3.6 mmol and Ca 1.6 mmol after the equilibration has occurred. pH is ~7.3. -------------------------------Phase assemblage-------------------------------- Moles in assemblage Phase SI log IAP log KT Initial Final Delta Calcite 0.00 -8.48 -8.48 1.000e+001 9.998e+000-1.646e-003 CO2(g) -2.00 -20.15 -18.15 1.000e+001 9.998e+000-1.976e-003 -----------------------------Solution composition------------------------------ Elements Molality Moles C 3.622e-003 3.622e-003 Ca 1.646e-003 1.646e-003 ----------------------------Description of solution---------------------------- pH = 7.297 Charge balance Here is a section of output for (4). In this problem, equilibrium_phases contains 10 moles of Calcite and 10 moles of CO2 and we want to react enough to attain a saturation index of -1 for calcite and a partial pressure of -2 for CO2. So the difference is that we want to attain a different saturation state for calcite in the resulting water. In the "Phase assemblage" output indicates SI=-1 for calcite and -2 (= log partial pressure) for CO2. However, to reach this state, 0.7203 (compare to 1.646) mmol of calcite dissolved; the amount of calcite decreased from 10 moles to 9.999. 1.059 mmol of CO2 dissolved. The concentration of C is 1.78 mmol and Ca 0.7 mmol after the equilibration has occurred. pH is ~6.95. -------------------------------Phase assemblage-------------------------------- Moles in assemblage Phase SI log IAP log KT Initial Final Delta Calcite -1.00 -9.48 -8.48 1.000e+001 9.999e+000-7.203e-004 CO2(g) -2.00 -20.15 -18.15 1.000e+001 9.999e+000-1.059e-003 -----------------------------Solution composition------------------------------ Elements Molality Moles C 1.780e-003 1.780e-003 Ca 7.203e-004 7.203e-004 ----------------------------Description of solution---------------------------- pH = 6.953 Charge balance SOLUTION 3 EQUILIBRIUM_PHASES 3 Calcite 0 0 CO2(g) -2.0 10 END > This third simulation is the again changes the saturation index of the calcite. The concentration is the same because the default is 10 moles. Check the output, is your statement correct? Your next questions are what is the pH effect of (1) calcite dissolution? (2) calcite precipitation? and (3) varying log PCO2 combined with calcite equilibrium? David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled

**References**:**Re: PHREEQC***From:*Elizabeth Delaney

- Prev by Date:
**Re: PHREEQC** - Next by Date:
**Modeling** - Previous by thread:
**Re: PHREEQC** - Next by thread:
**[no subject]** - Index(es):

Project Home Page

Complete Water Resources Division Software

USGS Home Page

Water Resources Division Home Page

NRP Home Page

Help Page